Fetch is my favorite FTP interface wise. Unlike the other FTP programs, it "LOOKS" like OSX. The features are "Mac like" and you can tell the designers of Fetch tried to make a seamless application to run within OSX. They succeeded.

Fetch can be ran as a trial, then purchased for $25.00 later if you decide you like it. IMO this is the most OSX compatible FTP made in both looks and performance.

CyberDuck supports Bonjour so that right off the bat is +1 for CyberDuck. Where I get the most use out of this program however is it's "get in, get out" simplicity. Cyberduck can be set to auto login to you iPhone as you start the program and the interface is a no frills, simplistic design made to operate at high speed. It's not pretty, It's not loaded with features, It's handy, quick, and ready to rock right when you need it. The majority of iPhone SSH'ers prefer Cyberduck for it's ease of use and Bonjour support. Cyberduck's K.I.S.S design (keep it simple, stupid) makes it the FTP for all....... and did I mention it's FREE? Open source design makes Cyberduck a favorite to keep in the apps folder even if you prefer another FTP program.

Need a full featured FTP client that does more? Transmit does what few others can in functionality by providing you with a dual window browser so you can grab files to drop on your iPhone without having to go hunting for them. Transmit will cost you $29.95 if you decide to keep it after your trial, but when you see how easy it is to drag from the dual browser, you might just decide to spend the coin.